Taking the crypt of a password is adding some weird foobar thing so that it doesn't equal

Question

#include <stdio.h>
#include <cs50.h>
#include <string.h>
#include <ctype.h>
#include <crypt.h>

int main(int argc, string argv[])
{
    if(argc > 2){ printf("too many arguments\n"); return 51; }
    if(argc < 2){ printf("too few arguments\n"); return 50; }
    //if(strlen(argv[1]) > 4){ printf("Password is greater than 4 characters\n"); return 52; }

    if(argc == 2) //make sure there are enough args
    {
        char hash_guess[] = "rofk";
        //long long counter = 0;

        //while(guess != argv[1]) //crypt(hash_guess, "50") != argv[1]) //while answer not correct
        //{
            for(int a = 65; a < 91; a++)
            {
                for(int b = 65; b < 91; b++)
                {
                    for(int c = 65; c < 91; c++)
                    {
                        for(int d = 65; d < 91; d++)
                        {
                            for(int A = 0; A < 9; A = A + 5) //control if first is caps or not
                            {
                                for(int B = 1 ; B < 9 ; B = B + 5)//control if second is caps or not
                                {
                                    for(int C = 2; C < 9; C = C + 5) //control if third is caps or not
                                    {
                                        for(int D = 3; D < 9; D = D + 5) //control if fourth is caps or not
                                        {
                                            hash_guess[0] = a;
                                            hash_guess[1] = b;
                                            hash_guess[2] = c;
                                            hash_guess[3] = d;
                                            hash_guess[A] = tolower(hash_guess[A]);
                                            hash_guess[B] = tolower(hash_guess[B]);
                                            hash_guess[C] = tolower(hash_guess[C]);
                                            hash_guess[D] = tolower(hash_guess[D]);
                                            printf("%s\n", hash_guess);

                                            string cryptoguess = (crypt(hash_guess, "50"));
                                            string input = argv[1];

                                            if( cryptoguess == input ) { return 0; }
                                        }
                                    }
                                }
                            }
                        }
                    }
                }
            //}
        //}
        //string guess = crypt(hash_guess, "50");
        //printf("%lli", counter);
    }
    }
}

I'm trying to make a program that goes through every 4 letter word, starting on aaaa and going to ZZZZ. I got that part done.

Part of the assignment is to encrypt that, and if the encryption matches an encrypted password, then you know you "hacked" their password. When I compare the encrypted password that I manually enter and the one that comes up by using the crypt function, they are the same, but in the debugger I see this for when it is encrypted by the computer:

"0x7ffff7dd9200 <_ufc_foobar+131200> "50k72iioeOiJU""

and the normal one that I enter shows

"0x7fffffffe34f "50k72iioeOiJU""

the same thing without the _ufc_foobar. Does anyone know why that is there and how I can get rid of it?

There's no foobar in your code? Is that exactly what it says? — M.M, Jul 06 '17 at 04:17
Are they just memory address offsets in the debugger? You are saying they "compare" the same right? What do you see when you print it to the console? — Alexander Higgins, Jul 06 '17 at 04:19
@Evert it is C, with the addition of tons of libraries. It's a course called CS50. — sruly, Jul 06 '17 at 04:19
By compare I think he means `if( cryptoguess == input ) { return 0; }` — Alexander Higgins, Jul 06 '17 at 04:19
@AlexanderHiggins when I check if they == it comes back as false, but when I look in the debugger they are identical other than the foobar stuff. — sruly, Jul 06 '17 at 04:20
@Evert if the pointers are equal shouldn't it come back positive? — sruly, Jul 06 '17 at 04:21
Are you on linux? (GNU)[http://www.gnu.org/software/libc/manual/html_node/crypt.html] defines the result of crypt as `char *` not string in which case use `strcmp` not `==` — Alexander Higgins, Jul 06 '17 at 04:22
@Evert I think you might be right, I remember learning about that when learning Java. How do I compare the contents of the pointers? — sruly, Jul 06 '17 at 04:23
@SrulyBrach it means the text `foobar` does not occur in your program. I'm wondering if you actually saw the exact characters `_ufc_foobar` on your screen, or if you actually saw something else but wrote _ufc_foobar instead. — M.M, Jul 06 '17 at 04:24
`strcmp` see this: https://stackoverflow.com/questions/7125697/c-comparing-pointers-with-chars — Alexander Higgins, Jul 06 '17 at 04:24
@M.M I saw it in the debugger, what I wrote was copy pasted. In the value of the int there was added _ufc_foobar — sruly, Jul 06 '17 at 04:25
@Evert that was it! Can you make that an answer so I can give you credit for it? — sruly, Jul 06 '17 at 04:28

score 1 · Answer 1 · answered Jul 06 '17 at 04:57

<_ufc_foobar+131200> isn't part of the string. It's your debugger attempting to figure out where the string came from, and assign a name to it. In this case, it's come up with a bogus result -- _ufc_foobar is the name of a function or variable somewhere else in the program, and your string happens to be stored 131,200 bytes (about 128 KB) after that in memory.

You can safely ignore this. Your strings are equal. They just happen to be stored in different parts of memory (which is normal).

score 1 · Accepted Answer · answered Jul 06 '17 at 05:00

The weird junk you are seeing is visualization of offsets of memory addresses in your code which can be ignored.

In your code you are using string when GNU specifies char * is the result of the crypt function.

Therefore, you cannot compare the pointers to the char array using == but instead need to use strcmp C comparing pointers (with chars)

For crypt see: http://www.gnu.org/software/libc/manual/html_node/crypt.html

Taking the crypt of a password is adding some weird foobar thing so that it doesn't equal

2 Answers2